The accurate reproduction of color images is very difficult because of the great color variation sensitivity of the human eye. Inks and toners of the same assumed color show variations from between different manufacturers and even between different batches. Maintaining color consistency over long press runs requires constant sampling and “eyeball” comparison of “pulled” samples to an original using special “daylight” illumination. Color copier color adjustments must be carried out to compensate aging of copier consumables and sub-assembly components.
The principle of blink comparison is well known in the field of astronomy, and optical blink comparators are used to identify anomalous astronomical events. A picture of the sky or portion of the sky at an earlier reference time provides a reference image. Astronomical comparisons are made of the same portions of the sky at a later time for discovering the subsequent occurrence of novae or other celestial events not present in the reference image. The discovery of the planet Pluto was made by Clyde Tombaugh in 1929 using a Carl Zeiss blink comparator.
According to one prior art method described in U.S. Pat. No. 4,404,590 (Ben Mayer et al, Sep. 13, 1983), a reference image is captured using a video camera while a comparison image or data image is imaged using a second video camera. The two images are superimposed at a low alternating frame rate on a video screen. Adjustments are carried out to geometrically align the two images and then any variation between the image pairs is detected as a blinking feature.